jonjon - By all means have a go at silverstone anyway, it's not that good for pics [nowhere particularly great to stand, nothing to pan against but the odd cone!] but it's still good practice. From looking at your other pics I'm sure you'll do really well anyway
Missy, you used shutter speed 1/4000?!
bring it down a little!!
As ross said it's mainly down to practice, keep trying diffrent speeds and you'll be fine.
I'm getting some more cash in soon so I'm going to buy myself a monopod so I can use even slower shutter speeds. Will hopefully get chance to go out and buy it before my next drift day.
Ross, how are you getting on with your photoshop? Post examples, please!!